First, he is only two. Second, some children do not really speak until they are three. Third, you may be siblings, but you are not clones. Each child is a unique entity. Give him some time. I am sure that with a loving big sister like you, he will be just fine.
What does your mother say about it? Is she concerned as well? Did he meet milestones on time such as crawling or walking?
How kind of you to be concerned for your little brother. It sounds like you have experience with kids and know what to expect.
Have your parents thought of having him evaluated by an Occupational Therapist?